Electromagnetic-thermal coupled modeling of internal temperature field in wood during microwave heating

Objective Microwave heating technology has shown great potential in wood processing due to its high efficiency. However, the relationship between distribution of microwave electric field and evolution of temperature within wood remains unclear. To address this issue, this study investigated the influence of microwave field distribution on internal temperature field in wood using numerical simulation.

Method A three-dimensional finite element model was established based on coupled electromagnetic and heat transfer theory. The model was used to simulate the electric field distribution within the microwave cavity and the temperature evolution inside wood under different microwave power levels (3.6, 4.5, and 5.4 kW). The accuracy of model was validated experimentally, with the simulation precision quantitatively evaluated using root mean square error (RMSE).

Result During the 30 second microwave heating process, the simulated temperature changes in the sub-surface and core layers of the wood agreed well with experimental measurements. The RMSE between simulation and experimental results increased with higher microwave power, reaching maximum values of 8.1 and 8.8 ℃ for the sub-surface and core layers, respectively, indicating high model accuracy. Microwave energy from different waveguides interfered and superimposed within the cavity, forming high- and low-energy zones. Reflections from the cavity walls further enhanced or weakened the electric field through interference, ultimately resulting in a standing wave effect and a spatially non-uniform electric field distribution. The difference in electromagnetic-to-thermal energy conversion efficiency between high- and low-energy zones led to varying heating rates within the wood. It demonstrates that the microwave field distribution directly governs the internal temperature evolution. Although the electric field distribution pattern remained consistent across power levels, higher microwave power significantly increased the maximum electric field intensity (p = 0.011). This accelerates the heating rate and enlarging the temperature difference between the surface and interior of the wood.

Conclusion This three-dimensional finite element model accurately predicts the electric field distribution and thermal response in wood under microwave heating. This study clarifies the electromagnetic-thermal coupling mechanism, providing a theoretical basis for optimizing wood microwave heating.